1. Field of the Invention
This invention relates generally to well head seals and, more particularly, but not by way of limitation, to a rolling-type well head seal assembly.
2. Description of the Prior Art
In general, wells utilizing surface power units rely upon conventional stuffing boxes to seal between the well head and the reciprocating pump rod. Normally these units utilize special pump rods, usually referred to as polish or polished rods, for that portion of the pump rod reciprocating adjacent to the stuffing box in order to minimize frictional wear. Often, polished rod protectors, such as that described in U.S. Pat. No. 3,796,103 are employed to prevent airborne abrasives from coming into contact with the polished rod/packing interface. However, the frictional wear between the packing in the stuffing box and the polished rod is still sufficiently great to require frequent adjustment and replacement of the packing.
In an effort to eliminate the frictional wear problem, various accordion type pump rod seals, such as that described in U.S. Pat. No. 3,369,411, have been devised to provide fluid tight sealing between the well head and the pump rod without using the stuffing box/polished rod combination. Such seals, however, are subjected to considerable longitudinal and radial flexing resulting in relatively rapid failure. In addition, such seals are generally incapable of withstanding high pressures due to the large surface area exposed to the pressure.